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| Joanna Groza | |
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email: jrgroza@ucdavis.edu |
| Office: 2007 Kemper Hall | |
| Phone: (530)752-8825 | |
| Professor | ||
| Ph.D., 1972, Polytechnic Institute, Bucharest | ||
Research  | ||
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| Consolidation of Nanocrystalline Powders: Nanocrystalline structures that include materials from metals to intermetallics and ceramics with less than 100 nm grain sizes hold the promise of unique physical and mechanical properties. Nanocrystalline powders are produced by using several processing methods such as mechanical alloying, sputtering or wet chemical techniques. These novel materials retain their unique properties if the initial metastable condition is preserved through the consolidation process. Generally, retention of these extremely fine structures requires a short time exposure at high temperatures. To accomplish this goal, either high pressure or physical activation of powder particle surface, such as in plasma activated sintering (PAS), may substitute for long time holding at high temperatures. Our research is directed towards gaining further insight into the mechanisms of nanoparticulate sintering and grain size evolution to retain the initial attractive microstructural features using high pressure (piston cylinder technique) or PAS. Typical nanocrystalline materials that are consolidated comprise metals (tungsten, iron, nickel), hard metals and composites (e. g., functionally graded materials). Mechanisms of Nanoparticle Consolidation: Our work in this area has been primarily focused on the understanding of the theoretical foundation of nanoparticle sintering mechanisms. Specifically, efforts are directed towards the investigation of the theoretical and experimental mechanisms by which nanopowders densify, such as pressure and surface activation roles. We expect to gain a better understanding of the latter issues by studying surface structure and neck formation in early sintering stages by direct in-situ heating experiments in TEM. Similar in-situ studies for the electrical field effects will be performed. The in-situ electron microscopy will be carried out at National Center for Electron Microscopy in Berkeley. Plasma Effects In Plasma Activated Sintering (PAS): Preliminary experiments indicated spectacular results in consolidation of difficult to sinter materials by PAS. Our major focus of the present PAS studies is to account for significantly shorter time than in conventional consolidation processes. Surface phenomena possibly generated by electrical field and effects on sintering behavior are being investigated experimentally and analytically. Processing- Microstructure- Property Relationships: The search for basic knowledge about the internal structure, properties, and processing of materials is a major, always evolving thrust in Materials Science. No real advancement in novel materials or processing can take place without the fundamental understanding of the chemistry-processing-microstructure-property relationship. Our research focuses on improving the basic knowledge of materials behavior in high-temperature, electrical field and fatigue conditions. Currently studied materials are high conductivity, high temperature strength dispersion strengthened alloys, tungsten and tungsten alloys. Some other potential areas of research involve the design of substitute materials that minimize air pollution upon metal casting. | ||
Laboratories | ||
| A modern mechanical alloying laboratory is equipped with two Spex Mills for small samples and one Szegvari attritor mill for larger mechanically alloyed batches. Equipment for producing vacuum, controlled and purified atmospheres is also available. A sophisticated metallographic microscope equipped with a microhardness indentor is available to assist initial microstructural studies. Shared facilities in Mechanical Engineering and Geology Departments are available for sintering studies using electrical field and high pressure application. A modern hot press with controlled atmosphere and very high temperature capability is installed in our Department and is used for parallel sintering studies. | ||
Support | ||
| National Science Foundation Industry | ||
Publications | ||
| PLASMA ACTIVATED SINTERING OF ADDITIVE-FREE AlN POWDERS TO NEAR-THEORETICAL DENSITY IN 5 MINUTES, J. R. Groza, S. H. Risbud, and K. Yamazaki, J. Mater. Res. 7(10):2643-2645, 1992. NANOPHASE STRUCTURE IN Nb-RICH Nb3Al ALLOY BY MECHANICAL ALLOYING, M. J. Tracy and J. Groza, Nanostructured Materials, 1:369-378, 1992. CLEAN GRAIN BOUNDARIES IN AlN CERAMICS DENSIFIED WITHOUT ADDITIVES BY A PLASMA-ACTIVATED SINTERING PROCESS S. H. Risbud, J. Groza and M. J. Kim., Phil. Mag., 69:525-533, 1994 LOW-CYCLE FATIGUE OF DISPERSION STRENGTHENED COPPER, J. Robles, K. Anderson, J. R. Groza, and J. C. Gibeling, Met. Mater. Trans, 25A:2235-2245, 1994 HIGH-PERFORMANCE DISPERSION STRENGTHENED Cu-8Cr-4Nb ALLOY, K. Anderson, J. R. Groza, R. D. Dreshfield and D. Ellis, Met. Mater. Trans, 26A:2197-2206, 1995 NANOPARTICULATE MATERIALS DENSIFICATION, J. R. Groza and R. J. Dowding, Nanostruct. Mat. 7:749-768, 1996 IRON-CEMENTITE NANOCOMPOSITE, T.J. Goodwin, S.H. Yoo, P. Matteazzi and J.R. Groza, Nanostructured Materials, 8:559-566, 1997 |
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